Clinical evidence of bacterial vaginosis was present in 25 (35%) of 72 patients attending a London venereology clinic and correlated significantly with abnormal organic acids in vaginal secretions (24/25), with Gardnerella vaginalis on culture (17/25), with complaints of vaginal malodour (15/25), and with a relative scarcity of white blood cells in vaginal secretions. Anaerobic vaginal flora were presumptively identified by gas-liquid chromatographic analysis of organic acids found in vaginal secretions. The clinical criteria used to diagnose bacterial vaginosis included the presence of at least three of the four following characteristics: (a) a vaginal pH greater than or equal to 4.5, vaginal secretions that (b) were homogeneous, (c) contained "clue" cells, and (d) released a "fishy" amine odour when mixed with 10% potassium hydroxide. Because 17 of the 25 patients with clinical bacterial vaginosis had both chromatographic bacterial vaginosis and G vaginalis, causative organisms were difficult to identify. None of the six patients who had G vaginalis but not chromatographic bacterial vaginosis had clinical bacterial vaginosis, but seven of the 10 women with chromatographic bacterial vaginosis but not G vaginalis had clinical bacterial vaginosis (p less than 0.02, chi 2 with Yates's correction). This finding supports the recent suggestions that anaerobes are important in the production of clinical signs of bacterial vaginosis.